PAPD7

Official Full Name

terminal nucleotidyltransferase 4A

Organism

Homo sapiens

GeneID

11044

Background

The protein encoded by this gene is a DNA polymerase that is likely involved in DNA repair. In addition, the encoded protein may be required for sister chromatid adhesion. Alternatively spliced transcript variants that encode different isoforms have been described. [provided by RefSeq, Jan 2010]

Synonyms

TENT4A; LAK1; POLK; POLS; TRF4; LAK-1; PAPD7; TRF41; TRF4-1; TUTASE5;

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Detailed Information

Molecular cloning and characterization of a novel isoform of the non-canonical poly(A) polymerase PAPD7

Seven proteins of the non-canonical poly(A) polymerases (ncPAPs) or the Cid1-like family contained in the Mammalian cells, as well as canonical poly(A) polymerases, were classified into the member of the polymerase β-like nucleotidyl transferase superfamily, which has homology in sequence and structure with the catalytic domain of DNA Pol β. A PAPD7-specific antibody was generated and it was found to be a protein migrated at 94 kDa on SDS-PAGE, whose isoform has N-terminal extension encoded by highly GC-rich sequence (>76%), the difference in intranuclear distributions of 94kDa PAPD7 from PAPD5 was revealed by fluorescent microscopy analysis: PAPD5 is widely distributed in the nucleoli and PAPD7 is excluded from it to accumulate into a minor pool in the cytoplasm. In the tethering assays for assay of the nucleotidyl transferase activities of those proteins, the 94kDa PAPD7 exhibited a robust nucleotidyl transferase activity than 62 kDa isoform when tethered to mRNA 3'UTR despite of both of which contain nucleotidyl transferase domain. Conserved residues of PAPD5 and PAPD7 N-terminal sequence were found to be in juxtaposition with nucleotidyl transferase domain, so the N-terminal region was narrowed to be an indispensable part for the nucleotidyl transferase activity and nuclear localization of PAPD7.

Protections provided by PAPD7 that ensure the integrity and stability of Hepatitis B virus RNA

Stabilization of hepatitis B virus (HBV) RNA can be got by interactions between the noncanonical poly(A) polymerases PAPD7 and the viral posttranscriptional regulatory element (PRE). It may represent a new antiviral target for control of HBV RNA metabolism, hepatitis B surface antigen (HBsAg) production, and viral replication. Antiviral therapy was developed by targeting these proteins. A potent chemical probe along with genetic analyses was utilized to dissect the individual roles of PAPD7 in HBV RNA stability. The chemical probe can inhibit PAPD7 enzymatic activities and reduces HBsAg both in vitro and in vivo. The essential role of stem-loop alpha sequence within PRE in HBV poly(A) tail integrity maintenance and determining sensitivity toward the inhibitory of this chemical probe has been demonstrated in genetic studies. Single PAPD7 KO did not cause any measurable changes within the HBV poly(A) tails, but both PAPD5 and PAPD7 KO in cells can induce reduced HBsAg production and resistance to this chemical probe.

Figure 1. A proposed model illustrating the interplay between HBV RNA cis-elements and the host factors PAPD5 and PAPD7 in maintaining HBV integrity and stability. (Fei Liu, et al. 2021)

References:

Liu F, Lee A C H, Guo F, et al. Host poly (A) polymerases PAPD5 and PAPD7 provide two layers of protection that ensure the integrity and stability of hepatitis B virus RNA. Journal of Virology, 2021, 95(18): e00574-21.
Ogami K, Cho R, Hoshino S. Molecular cloning and characterization of a novel isoform of the non-canonical poly (A) polymerase PAPD7. Biochemical and biophysical research communications, 2013, 432(1): 135-140.

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